An X-ray computed tomography (to be referred to as a CT hereinafter) apparatus includes an X-ray tube which generates X-rays, an X-ray detector which detects X-rays, a movable top on which an object is placed, and an image processing unit which scans the object placed on the top with X-rays while rotating the X-ray tube and the X-ray detector and generates image data by reconstructing the projection data acquired by this scan.
An X-ray CT apparatus has scan modes, e.g., a scan mode of continuously acquiring projection data by irradiating an object with X-rays while moving the top and a scan mode of acquiring projection data by irradiating the object with X-rays while stopping the top. The operator sets a scan mode in accordance with an examination. When executing a plurality of scans in an examination, an operator sets a plan for executing the plurality of scans. There is known an expert plan which allows to sequentially execute the plurality of scans based on the set plan.
If, however, system down occurs in the X-ray CT apparatus due to a power failure or the like in the process of executing scans based on the expert plan, it is necessary to redo from the first scan. This leads to an increase in the exposure dose on the object.